Question about 1979 Yamaha XS 650 SF

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My '79 xs650 is popping thru the exhaust. It was fine last year except for leaking petcocks. I cleaned the taps and put new K&L kits in each side. Still have some trouble with leak thru to the carbs. Bike sounds like it has a lean condition. I removed the carbs, dismanteled them and soaked them for 4 hrs. in a carb cleaning solution. Blew out all passages with compressed air but no help.

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  • David Parker
    David Parker May 11, 2010

    please remove and check colour of your plugs and come back to me



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Reset float levels and make sure that your needle and seat is not leaking and check that you have no air leaks on your inlet rubbers.

clean the carb properly and remove all fuel jets , needle jet and air screws before blowing out.

Posted on Aug 06, 2009

  • David Parker
    David Parker Aug 11, 2009

    Hope I have resolved you question, but please leave positive feedback if so , as it still takes time to answer questions and it would just be nice to know if I have helped.



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My 1996 oldsmobile cutlass supreme runs rough, no power, has new egr valve. whats next?

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I have a yamaha ttr 125 it run good for a few hours then dies and wont start

i dont think you need a new carb but if you are already getting one this is fine you need to find out what jets are in it or you can get jet kits for your carb and change them yourself they come with instructions. with it running for a while just fine and then dies this sounds like you may have water in the gas or dirt in the carb bowl to check for dirt get a clean empty water botter clear one put the hose from bottom of carb in bottle and open the bleeder screw on the bottom of the carb bowl if there is dirt or water you will see it in the bottle empty the bowl then turn on the gas petcock let a bit more run through shut of petcock and close the bowl screw , if you see dirt then you should clean the carb remove and rebuild while you are doing this you can install larger jetting good luck

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What kind of gas does my 1979 Yamaha XS650 Special II take?

Hi, Anonymous for this scenario you will need your service/owners manual if you can't find the first and best tool you ever bought for your Yamaha, despair not, for a mere zero $0 you can download another one.
For more information about your issue and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day.
What octane gas do you use
Yamaha Petcock Fuel Gas Tap Valve Right Left XS650 XS750 Special XS850...
Yamaha XS650SE Shop Manual
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Apr 09, 2012 | 1979 Yamaha XS 650 SF

1 Answer

Fuel over flows thru overflow tubes only when motor is running. motor off ignition on it stops.

Your gas tank petcock is diaphram operated.
there is a vacuum line coming off the intake, that goes straightb to the petcock.
when you turn the motor over a vacuum is created, pulling the petcock diaphram back and allowing fuel to flow to your carburetor. when you turn the motor off the vaumm is gone and the spring behind the diaphram pushes it closed and stops the fuel flow to the carbs.

Now the reason the carbs are overflowing is because the floats valves are not closing, in other words the floats are sticking.
Usually a good carb clean will cure the problem, especially for that year.
the older ones usually require new float valves/seats that are usually found in a good carb rebuild kit. You shouldn't need one.

If your really broke try tapping on the bowls of the carburetor lightly, while the engine is running, sometimes the vibration will vibrate a particle loose that may be holding open the float valve.
if it works then the fuel should stop overflowing while running.

if you know how to work on it, try this, with the engine off.
open the carburetor drain screws so that fuel will run out the carb. drain. flush out the carb.
get a container to catch the gasoline.
while fuel is flowing tap the carb bowls a few times then closed the drain screws.
clean up any spilled gasoline .
start your bike.see if they stop leaking and the floats are closing.
if it still leaks, you'll need the cleaning.

Happy Riding
Best Regards
Big Al

May 22, 2011 | 1997 Yamaha Royal Star XVZ 1300 A

1 Answer

Have a 1997 Yamaha Virago 1100 cc, started it for the first time this year and found fuel leaking out of my overfill line,so therefore changed oil and filter, spark plugs, not leaking as much now, but...

One thing you might check....not real familiar with Viragos....but if your bike has the vacuum petcock...make sure the diaphragm isn't leaking and your vacuum line isn't sucking fuel into the intake.

As for the floats...if the petcock is fine....sometimes tapping the flat bowl of an overflowing carb with the plastic handle of a large screwdriver will free the float.

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2 Answers

2005 1200 s. Since not being ridden for 6 to 8 weeks,gas has leaked into crank case.Fuel tap has no shut off,so I assume there must be a vaccume activated diafram,of sorts,in the tap.Could this be...

Either the vacuum operated petcock is stuck in the flow position as well as a float needle is stuck in the open position. Two things would have to be wrong so that the fuel would over flow the carburetors and run past the piston rings into the crankcase. Or, more likely, the vacuum diaphragm inside the fuel petcock is leaking and the fuel is flowing down the vacuum line into the engine. I would start by inspecting the vacuum fuel petcock. If you unplug the vacuum line and gas is dripping from the vacuum line then you will need to rebuild or replace the fuel petcock.

Mar 06, 2011 | 2005 Suzuki GSF 1200 Bandit S

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Pops through exhaust when throttle is shut down . 79 1000 ltd. aftermarket exhaust,kn filters, stage3 jet kit

check vacuum pipes are not leaking. if you have removed airbox for K&N cone filters then vacuum tubes need to be sealed.

Mar 12, 2010 | 1981 kawasaki KZ 1300 A3

1 Answer

2002 xjr1300 fuel tap leak

You can get a petcock rebuild kit if this is what your fuel tap refers to.

Aug 03, 2009 | 1999 Yamaha XJR 1300

2 Answers

No power when going into 2nd gear or higher

Forget the wiring. The key thing here is probably the painted gas tank. In all likelihood there was some trash that got into the tank related to the paint job. Do this > Carefully remove the water trap bowl from the petcock, (gas valve), and look inside the bowl. It may have some water in the bottom and some trash on top. Clean the bowl. Next, remove the petcock and clean it as well. Drain the carbs. Turn the gas on and wait a minute for the float bowls to fill.

Give it a try. It may be that the gas from the tank is restricted and can't refill the floats as fast as the engine needs. A second thought is the exhaust pipe. The bike will not run well if the exhaust is partly plugged up. Disconnect the exhaust and tick off the neighbors by going around the block without a muffler. The inside of the muffler may have collapsed when the welding was done.

Between the two solutions I think the exhaust is the more likely.
Please rate this solution as " FixYa " if you go riding tomorrow.

Mar 24, 2009 | 1982 Yamaha XJ 650

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